1. Field of the Invention
The present invention relates to a Micro Electro Mechanical System (MEMS) device and a fabrication method thereof. More particularly, the present invention relates to an electrostatic driving MEMS device having a driving electrode in an embedded structure and a fabrication method thereof.
2. Description of the Related Art
Micro Electro Mechanical System is a technology that implements mechanical and electrical parts, using semiconductor processing techniques. A conventional MEMS device generally includes floating driving parts that are movable over a substrate in order for the device fabricated using MEMS technology to perform mechanical operations.
FIG. 1 illustrates a cross-sectional view schematically showing a conventional MEMS device. The conventional MEMS device of FIG. 1 includes a substrate 10, a fixing part 30 attached to the substrate 10, and a driving part 40 extending from the fixing part 30. The fixing part 30 is generally referred to as an anchor or a support. The fixing part 30 connects the driving part 40 to the substrate 10.
The driving part 40 is spaced to float over the substrate 10. The driving part 40 is movable in an upward and downward direction, as shown by the broken lines in FIG. 1. The movement of the driving part 40 is controlled by a predetermined driving force from an electrode part 20 formed on the substrate 10. The driving part 40 is typically fabricated in a shape such as a beam, a membrane, or the like depending on device requirements.
FIG. 2A to FIG. 2E illustrate views for sequentially illustrating stages in a process for fabricating a conventional electrostatic drive-type RF MEMS device.
As shown in FIG. 2A, a driving electrode layer 220, for providing an electrostatic driving force, is formed on a substrate 210 through patterning. In FIG. 2B, a metal layer is formed on the substrate and then the metal layer is patterned so metal layer areas 230 having similar shapes remain. The metal layer areas 230 are an anchor part to acts as a fixing part fixed on the substrate 210 and an RF line to act as input and/or output terminals of an RF signal. The metal layer areas 230 are formed in a thick layer having a thickness of 2 to 3 μm in consideration of the skin depth effect.
Next, referring to FIG. 2C, an insulation layer 240 is formed to surround the driving electrode layer 220 formed on the substrate 210.
Thereafter, as shown in FIG. 2D, a sacrificial layer 250 is formed on the resultant structure on the substrate 210. The sacrificial layer 250 over the anchor part fixed on the substrate 210 is etched through predetermined patterning. Referring to FIG. 2E, a MEMS structure layer is then formed on the patterned sacrificial layer 250. The MEMS structure layer includes a driving part 260 and a connection part 261.
Subsequently, predetermined etching access holes (not shown) are formed in the driving part 260 of the MEMS structure layer, and an etchant is supplied through the etching access holes to selectively etch only the sacrificial layer 250. Accordingly, as shown in FIG. 2E, a conventional MEMS device is fabricated such that the driving part 260 floats over the substrate 210 after the removal of the sacrificial layer 250.
As stated above, a conventional fabrication process proceeds regardless of a step-height difference between the metal layer areas 230 and the driving electrode layer 220. Consequently, a step-height difference between the metal layer areas 230 and the driving electrode layer 220 causes the driving part 260, which is formed by a subsequent procedure, to be formed unevenly, as may be seen in FIG. 2E. Thus, the reliability of such a MEMS device decreases. Moreover, since unevenness of the driving part is not expected during the designing of the device, a significant error exists between the design of the device and the fabrication process. Further, unevenness in the driving part 260 causes a problem in that the driving of the driving part 260 may be incomplete when the MEMS device is driven.
Further, in the stages of the fabrication process shown in FIGS. 2D and 2E, the connection part 261 of the MEMS structure layer, which is formed on an anchor part and the substrate 210, is formed in a bent shape that is relatively thinner than the anchor part and the MEMS structure layer.
Accordingly, the connection part 261 having a thin and bent shape causes a problem in the stability of the MEMS device, since the general operation of the MEMS device involves the movement of the MEMS structure, i.e., the driving part 260.